Field of the Invention
This invention relates to a method of improving the archival properties of a processed photographic film and to a storage assembly for such film.
The archival properties of processed photographic films are an important aspect for all types of photographic films, and are even more important with respect to motion picture photographic films. The archival keeping properties of photographic films are expected to be measured by decades and even in certain instances by centuries. Such time periods of course cannot be determined by natural measurements but are accurately predicted by Arrhenius estimations.
It has been a common practice to use hermetically sealed containers including tin-plated or painted metal (iron) cans, plastic cans, cardboard boxes and the like to store processed motion picture films to extend their useful life under controlled humidities and temperatures. Storage of films in metal cans offers the best moisture protection and generally prevents attack on image silver and image dyes by vapor phase chemical contamination from atmospheric pollutants. The ANSI (American National Standard for Imaging Media) IT9. 11-1992 standard on storage of processed photographic films requires that the relative humidity be maintained between 20 and 30% RH and that the maximum temperature of storage shall not exceed 21.degree. C. for black and white films, while the storage of color films shall not exceed 2.degree. C. It is imperative that both the relative humidity and the temperature during storage are maintained to insure the expected longevity of the imaging media and for the subsequent retrieval, projection and duplication of the recorded information. Because of the complex nature of photographic films, the various mechanisms for attack on the film that reduce the archival properties of the film are both numerous and complex. Open storage under atmospheric conditions, while suitable to prevent degradation from some forms of attack, is not only impractical, but also results in attack from atmospheric contaminants such as hydrogen peroxide, sulfur dioxide, ozone, moist oxygen, nitrogen oxides, and other species which attack the image silver in black and white films. The image dyes are susceptible to fading when exposed to high intensity light or elevated temperatures and humidities and hence require fairly low temperatures and humidity during storage. Dye fading reactions under confined storage conditions result from various and numerous mechanisms including film support degradations, which have become known as the "vinegar syndrome" resulting in the liberation of acids which decrease the life of the film. The presence of moisture also creates archival disadvantages since the presence of moisture acts as a protoic catalyst that increases the rate of deacetylation and the step wise elimination of acetic acid from cellulose riacetate supports. Thus, the presence of moisture accelerates the vinegar syndrome effect which in turn decreases the pH within the environment of the stored film and this in turn results in the dye fading of the photographic element being stored.
In addition to the presence of the materials mentioned above, in closed containers wherein photographic elements are stored for archival purposes, the presence of solvents employed in the manufacture of the photographic film also creates problems in that these materials can disadvantageously affect the photographic properties of the film.
Thus, the archival properties of a processed photographic film stored within the closed container are inherently dependent upon the environment within the container and the changes that are continually occurring with respect to the various layers present in the processed film. These various changes working either alone or together result in alterations to the film which are undesirable and require correction.